Pathogenic bacteria require iron for their survival and ability to cause infection. Heme comprises 90% of the iron available within the host and plays a significant role in the colonization and virulence of many bacterial pathogens. Shigella spp. and enteroinvasive E. coli are responsible for shigellosis in humans, a disease characterized by the destruction of the mucosal layers of the colon. S. dysenteriae is particularly problematic as it produces a more severe form of the disease and is associated with life threatening complications. The recent increase in the emergence of drug resistance has severely limited the choice of antimicrobial agents available. A shift in strategy for antimicrobial development has been to focus on antimicrobial targets that are not essential for bacterial survival, but are required for virulence, thus reducing the selective pressure for development of drug resistance. The ability to acquire iron from the host is one of the most important and well understood determinants of bacterial virulence and pathogenesis. Recently it has been shown in a number of organisms that heme is an essential source of iron during infection and disease progression. Therefore, targeting heme uptake and utilization alone or in combination with other antimicrobial approaches may provide a novel therapeutic strategy. The overall goal of the studies are; i) To characterize the heme uptake proteins utilizing a combination of site-directed mutagenesis, crystallographic and spectroscopic techniques to determine heme binding properties of the heme uptake system. ii) To determine the mechanism of heme transport through the bacterial outer membrane to the cytoplasm utilizing in vitro model systems in proteoliposomes; and iii) to determine the role of the cytoplasmic heme binding protein ShuS in intracellular heme metabolism through proteomic and metabolomic studies. These studies will provide a thorough understanding of the molecular mechanisms of heme uptake and utilization in gram-negative pathogens as a step toward identifying therapeutic targets for future drug design and development. PUBLIC HEALTH RELEVANCE: The need for new therapeutics targeting enteric pathogens such as Shigella dysenteria is a high priority given the increase in resistance to current antibiotics. S. dysenteriae the causative agent of shigellosis, is responsible for 160 million outbreaks per year and has a high rate of morbidity and mortality in developing countries. Of the estimated 1.1 million deaths per year 60% occur in children under the age of 5 years. Heme utilization by S. dysenteriae is required for virulence and characterization of heme uptake and metabolism may provide novel therapeutic targets for drug development.